1993 BMW 325i Workshop Manual

SUSPENSION,
STEERING
ANDBRAKES-GENERAL



300-1

300
Suspension,
Steering

and
Brakes-General

GENERAL
.....
.
....
.
.....
.
.
.
........
.300-1



M3
SUSPENSION
AND
BRAKES
.......
.
...
300-7

Front
Suspension
..........
.
.
.
...
.
.....
300-1

Steering
...
.
.
.
.
.
....
.
.
.
...
.
.
.
...
.
...
.
.
300-2



SUSPENSION
AND
STEERING

Rear
Suspension
....
.
.
.
...
.
.
.
...
.
.....
300-2



TROUBLESHOOTING
..
.
.
.
.............
300-7

Brakes
.
.
.
.
.
.
.
.
....
.
...........
.
.
.
.
.
.
300-2

Tires
and
wheeis
.
................
.
.
.
.
.
.
300-2



TABLE

a
.
AST
Indicator
Lamp
Function
..
..
.
..
.
.........
300-5

INTEGRATED
SYSTEMS
.........
.
.
.
.
.
.
300-2



b
.
Suspension
and
Steering
Troubleshooting
......
.300-8

Antilock
Brake
System
(ABS)
.......
.
.
.
.
.
.
300-2

Al¡
Season
Traction
(AST)
.........
.
.
.
.
.
.
300-4

GENERAL



Front
Suspension

This
section
covers
general
information
for
front
and
rear



The
lower
control
arms
connect
the
front
suspension
struts

suspension,
the
steering
system,
and
the
brakíng
and
traction



to
mounting
points
on
the
subframe
crossmember
and
the

control
systems
.



body
.
See
Fig
.
2
.

The
BMW
E36
suspension
and
steering
systems
are
engi-

neered
to
provide
a
compromise
between
taut,
responsive
handling
and
ride
comfort
.
Although
the
front
and
rear
suspen-
sion
assemblies
are
independent
subsystems,
they
work
to-

gether
to
achieve
BMW's
overall
combination
of
precise

handling
and
comfort
.
See
Fig
.
1
.

Fig
.
1
.



BMW
E36
front
and
rear
suspension
systems
.

Each
front
strut
assembly
includes
a
shock
absorber
car-

tridgeinside
the
tubular
strut
housing
and
a
large
coil
spring
.

The
upper
strut
mount
bearing
allows
the
strutto
turnwith
the

wheels
.
The
lower
end
of
the
strut,
which
includes
the
stub
axle
for
the
front
wheel,
connects
to
a
ball-joint
on
the
control
arm
.

0013098

GENERAL

300-2



SUSPENSION,
STEERING
AND
BRAKES-GENERAL

Steering

INTEGRATED
SYSTEMS

The
steering
linkage
connects
the
rack-and-pinion
unit
through
tie
rodsto
the
steering
arms
.
The
tie
rod
ends
allow
the
wheels
to
pivot
and
react
to
suspension
travel
.

Rear
Suspension

The
rear
axle
carrier
is
the
main
mounting
point
for
the
final

drive
housing
and
the
rear
suspension
components
.

Trailing
arms
locatethe
rear
wheels
and
anchorthe
springs,

shocks
and
stabilizer
bar
.
Driveaxies
with
constant-velocity

(CV)
joints
at
both
ends
transfer
power
from
the
differential
to

the
road
wheels
.
The
differential
is
mounted
to
the
rearaxle

carrier
through
rubber
mountsand
bushings
to
hele
isolate

drivetrain
noise
and
vibration
.

Brakes

E36
cars
areequipped
with
power
disc
brakes
with
an
inte-
gral
antilock
brakes
(ABS)
.
The
parking
brake
is
a
dual-drum

system
integrated
with
the
rear
brake
rotors
.
See
Fig
.
3
.

Power
assist
is
provided
by
a
vacuum
booster
when
the
en-

gine
is
running
.
The
brakepedal
pushrod
is
connected
directly

to
the
master
cylinder,
so
failure
of
the
vacuum
booster
does

not
normally
result
in
total
brake
failure
.

0012124



Each
disc
brakeuses
a
caliper
with
a
single
hydraulic
cylin-
Fig
.
2
.



Front
suspension
control
arm
(arrow)
.



der
.
Brake
pads
in
the
left
front
and
right
rear
contain
wear

sensors
.
When
the
padsneed
replacement,the
sensors
illu-
The
front
suspension
is
designed
with
minimum
positive



minate
a
light
on
the
dashboard
.
steering
offset
.
This
geometry
contributes
to
stability
when

traction
is
unequalfrom
side
to
side
.
Suspension
travel
is
lim-



Tires
and
Wheels
ited
by
rubber
bump
stops
.

The
three
point
mounting
of
each
L-shaped
control
arm
ere-



Tiresize
is
critica¡
to
the
proper
operatíon
of
the
E36
ABS
or

cisely
controls
the
front-to-rear
and
side-to-side
position
of
the



ABS/AST
system
.
Severa¡
different
styles
of
wheels,
in
15,16

strut,
while
the
flexibility
of
the
joints
and
mounts
alsoallows



and
17
inch
diameters,
are
available
from
an
authorized
BMW

the
movement
necessary
for
suspension
travel
.
The
control



dealer
.

arm
mounting
points
are
designed
with
anti-dive
geometry
.

The
suspension
reduces
the
normaltendency
for
the
front
of



NOTE-
the
vehicle
to
dive
under
hard
braking
.



Aftermarket
wheelsshould
be
selected
wlth
care
.
Im-
properly
fitted
wheels
can
contact
anddamage
sus

Control
arm
position
is
fixed,
with
no
adjustment
provisions



pension,
brakeorbodycomponentsandmayadversely

on
the
control
arms
for
alter¡ng
front
wheel
al
ignment
.
A
stabi-



affect
vehicle
stability
.

lizer
bar
mounted
to
both
control
arms
heles
to
reduce
body
rol¡
whencomering
.



INTEGRATED
SYSTEMS

Antilock
Brake
System
(ABS)
is
standard
on
all
E36
cars
.

The
variable-assist
power
steering
system
consists
of
an



Standard
on
some
models
and
installed
as
optional
equipment
on

engine-driven
hydraulic
pump,
a
rack-and-pinion
type
steer-



others,
is
All
Season
Traction
(AST)
.

ing
gear,
and
connecting
linkage
to
the
road
wheels
.
TheE36
utilizes
an
engine-speed
dependent
variable
effort
steering



Antilock
Brake
System
(ABS)

system
.
At
low
speeds,
maximum
power
assist
is
provided
to
ease
parking
and
city
driving
.
Athigh
speeds,
assist
is
re-



The
electronically-controlled
ABS
maintains
vehícle
stabili
duced
to
ensure
stability
.



ty
and
control
during
emergency
braking
by
preventing
wheel
lock-up
.
ABS
provides
optimum
deceleration
and
stability
dur-

Wheel
brake
caliper

Electronic
control
module
Fig
.
4
.



Schematic
representation
of
ABS
.

SUSPENSION,
STEERING
ANDBRAKES-GENERAL



300-3

Fig
.
3
.



Schematic
view
ofdual
circuit
brakes
with
4-channel
ABS
.

ing
adverse
conditions
.
It
automatically
adjusts
brake
system
hydraulic
pressure
at
each
wheel
to
prevent
wheel
lock-up
.

The
system's
main
components
arethe
wheel
speed
(pulse)
sensors,
the
ABS
control
module,
and
the
hydraulic

control
unit
.
See
Fig
.
4
.

Warning
lamp

u
Master

Whee

_

l
speed



I-lydraulic



cylinder

sensor



control
unit



0012135

UNI

The
wheel
speed
sensors
continuously
send
wheel
speed
signals
to
the
control
module
.
See
Fig
.
5
.
The
control
module
compares
these
signals
to
determine,
in
fractions
of
a
second,
whether
any
of
the
wheels
areabout
to
lock
.
If
any
wheel
is
nearing
a
lock-up
condition,
the
module
signals
the
hydraulic
unit
to
maintain
or
reduce
pressure
at
the
appropriatewheel(s)
.
Pressure
is
modulated
by
electrically-operated
sole-

noid
valves
in
the
hydraulic
unit
.

Fig
.
5
.



ABS
wheelspeed
sensor
.

0006563

INTEGRATED
SYSTEMS

300-4



SUSPENSION,
STEERING
AND
BRAKES-GENERAL

Three-channel
ABS
ís
used
on
al[
E36
cars
equipped
with



Al¡
Season
Traction
(AST)
standard
ABS
.
Each
front
wheelhas
a
separate
solenoid

valve
to
modulate
hydraulic
pressure
to
that
brake
caliper
.



The
traction
control
system
works
in
conjunction
with
ABS
The
rear
wheels
are
modulated
asa
pair,
controlled
by
a
sin-



and
the
engine
management
system
to
enhance
vehicle
con
gle
solenoid
valve
.



trol
.
The
main
function
of
the
AST
system
is
to
maintain
the
rolling

contact
between
the
tires
and
the
road
surface
under
al¡
driving
E36
cars
equipped
with
ABS/AST
utilize
a
four
channel
sys-



conditions
.
This
is
achieved
through
exact
application
and
tem,
which
functionsexactly
as
the
three
channelsystem



management
of
braking
and
drivetrain
forces
.
above,except
that
the
rear
wheels
are
modulated
individually
.

IDLE
SPEED
CONTROL
VALVE

HROTTLE
PLATE

6
.

Í
III

i



ADS
ACTU
AT
OR

THROTTLE
PLATE
POSITION
SENSOR

DME

Fig
.
6
.
All
Season
Traction
(AS)
works
withother
drivetrain
systems
to
enhance
vehicle
control
.

INTEGRATED
SYSTEMS

The
throttle
control
system
used
in
AST
is
illustrated
in
Fig
.

MASS
AIR
FLOW
SENSOR

JADS
THROTTLE
PLATE
POSITION
SENSOR

0013006

NOTE-

The
traction
control
system
referred
to
as
AST
(all
sea-
son
traction)
may
also
be
referred
to
as
ASC
(Automat-
ic
Stability
Control)
and
ASC+T
(Automatic
Stability
Control+Traction)
.

The
AST
system
improves
traction
by
electronically
apply-

ing
the
rear
brakes
when
therear
drive
wheels
are
spinning
at

a
faster
rate
than
the
front
wheels
.
The
combined
ABS/AST

control
module,
operating
through
the
ABS
hydraulic
control

unit,
modulates
braking
force
at
therear
wheels
.

In
addition,
AST
uses
retarded
ignition
timing
and
an
auxil-iary
engine
throttle
plate
to
reduceengine
torque
and
maintain

vehicle
stability
.

The
auxiliary
throttle
plate
is
held
open
by
spring
pressure
.

The
AST
system
actívates
the
auxiliary
throttie
position
motor

(ADS)
to
cose
the
AST
throttle
as
needed
.
This
reduces
the

volume
of
engine
intake
air
.
Due
to
the
throttle
closing
very
rapidly
during
AST
operationthe
driver
cannot
increase
theengine
power
output
regardless
of
how
far
theaccelerator
pedal
is
pushed
to
the
floor
.

The
auxiliary
throttle
plate
is
placed
ahead
of
the
conven-

tional
throttle
plate
in
the
throttle
body
.

Traction
control
also
comes
into
operationduringdecelera-
tion
.
Decelerating
on
snowy
or
icy
road
surfaces
can
lead
to
rear
wheel
slip
.
If
a
rear
wheel
startsto
drag
or
lock
up
when

the
throttle
is
closed
rapidly
orduringdownshifting,the
AST
system
can
limit
the
problem
by
advancing
the
ignition
timing
.

A
switch
on
the
center
console
is
used
to
togglethe
AST
on

or
off
.

The
AST
system
is
designed
to
be
maintenance
free
.
There

are
no
adjustments
that
can
be
made
.
Repair
and
trouble-
shooting
of
the
AST
system
requires
special
test
equipment

andknowledgeand
should
be
performed
only
by
an
autho-

rized
BMW
dealer
.
Table
a
lists
theconditions
indicated
by

the
AST
indicator
light
in
the
instrument
cluster

SUSPENSION,
STEERING
AND
BRAKES-GENERAL



300-5

Tablea
.
AST
Indicator
Lamp
Function

Indicator
lamp



1
Condition



1
Comment

Light
on



Normal
AST
start-



Automatic
AST
up



self-test

Light
off



AST
monitoring



Automatic
AST
op-
mode



eration

Press
AST
button,



AST
off
(disabled)



Rocking
the
car
tolight
comes
on



getout
of
snow
or
other
loose
surface
Driving
with
snow
chains

Press
AST
button
:



AST
monitoring



Automatic
AST
op-
light
goes
out



I
mode



eration

Light
flashes



AST
active
mode



I
Normal
AST
oper-
ation
as
it
controls
wheel
speed

Light
stays
on
af-



Defect
in
AST



Consult
BMW
ter
start
up
or



dealer
for
diagno-
comes
on
while



sis/repair
driving



(Vehicle
operation
remains
normal)

WARNING
-

Even
a
car
with
AST
is
subject
to
the
normal
physi-
cal
laws
.
Avoid
excessive
speeds
for
the
road
con-
ditions
encountered
.

CAUTION-
"
If
the
tires
on
the
carare
of
different
makes,
the
AST
system
may
over-react
.
Only
fit
tires
of
the
same
make
and
tread
pattem,

"In
adverse
conditions,
such
as
trying
to
rock
the
car
outof
deep
snow
or
another
soft
surface,
or
when
snow
chainsare
fitted,
it
is
advisable
to
switch
off
AST
and
allow
the
cars
driveline
to
op-
erate
conventionally
.

INTEGRATED
SYSTEMS

300-6



SUSPENSION,
STEERING
AND
BRAKES-GENERAL

BATTE
RY

KL
30

ECM
MAIN
C~
RELAY



KL
15

DSC
SWITCH

LF1
;1~lZZ~



nSLn

l'
z
sJ



WHEEL

RF

c_
.

LR

r_
.
>
RR

ELECTRONIC
BRAKE
LIGHT
SWITCH

SPEED

SENSORS

Fig
.
7
.



Schematic
of
AII
Season
Traction
(AST)
system
.

INTEGRATED
SYSTEMS

EDC

POWER
SUPPLY



SOLENOID
RELAY
GROUND
CONTROL

POWER
SUPPLY
I'
1
ABS
PUMP

GROUND
CONTROLÍ
F



f
iJ
RELAY

INLET
(4X)
wxxuw
OUTLET
(4X)



-=-=--



AST
AST
INTAKE
IHYDRAULIC
-
=-

SWITCHING
=---

!
99001
!J

WHEEL
SPEED
X
4

DME
II

000001
-
f



1
UNIT

AGS

IKE
&
DMEI
PARK
BREVE

771
SWITCH

M
ALTERNATOR



AUXILIARY
THROTTLE

r
`



INDICATOR



POSITION
MOTOR
(ADS)

ABSPUMP



DIAGNOSIS

RELAY



lu~~~b

0013027

increased
power
output
and
road-handling
demands
.

The
steering
geometry
is
modified
by
changing
the
cast-

er/camber
angles
slightly
.
This
is
accomplishedby
reposition-

ing
the
upper
strut
mounting
holes
in
the
frontstrut
towers
and

through
different
front
and
rear
control
arms
.

M3
Brake
System
Improvements

"
Vented
directionalfront
rotors
:
315
mm
dia
.
x
28
mm
thick
.

"
Vented
directional
rear

rotors
:
312
mm
dia
.
x20
mm
thick
.

"
Larger
brake
pads
and
calipers
.

"
Modified
Teves
ABS
system
.

SUSPENSION,
STEERING
AND
BRAKES-GENERAL



300-
7

M3
SUSPENSION
AND
BRAKES



NOTE-

M3
brake
rotors
are
directional,
having
a
different
part

TheE36
M3
was
introduced
in
late
1994
as
a
1995
model
.



number
for
each
side
.
Rotors
with
an
odd
part
number

The
design
of
the
M3
suspension,
steering
and
brakes
is
a



go
on
the
left
while
rotors
with
en
even
part
numbergo

modification
of
existing
E36
systems
which
accommodates



on
the
right
.

M3
Front
SuspensionImprovements

"
Reinforced
spring
plates,control
arms,
control
arm
bush-

ings,
steering
arms
.

"
Recalibrated
struts,
firmer
springs
.

"
Stiffer
stabilizerbar,
larger
stabilizer
bar
bushings
.

"
Front
stabilizer
linked
to
struts
.

M3
Wheels/Tires

"
Front
wheels
1992-1998
:.....
7
.5J
x
17
in
.
light
alloy

"
Rear
wheel
1992-1997
.......
7
.5J
x17
in
.
light
alloy

"
Rear
wheel
(option)
........
.8
.5
Jx17
in
.
light
alloy

"
Front
and
rear
tire

1992-1997
.............
.
.
.
...
...
235/40
x
17
in
.

"
Front
tire
1998
only
......
...
.
.
.
...
225/45
x
17
in
.

"
Rear
tire
1998
only
.......
.
.
.
...
...
245/40
x
17
in
.

CAUTION-

In
en
emergency,
an
M3
front
wheel/tire
assembly
may
be
mounted
on
the
rearaxle
.
However
a
rear
wheel/tire
assemblymust
not
be
mounted
on
the
front
axle
.

M3
RearSuspensionImprovements

"
Reinforced
trailing
arms
.

"
Recalibrated
shock
absorbers,
firmer
springs
.



SUSPENSION
AND
STEERING

TROUBLESHOOTING

Stable
handling
and
ride
comfort
both
depend
on
the
integ-

rity
of
the
suspension
and
steering
components
.
Any
symp-

tom
of
instability
or
imprecise
road
feel
may
be
caused
by

worn
or
damaged
suspension
components
.

When
troubleshooting
suspension
and
steering
problems,

also
consider
the
condition
of
tires,
wheels,
and
their
align-

ment
.
Tire
wear
and
incorrect
inflation
pressures
can
dramati-

cally
affect
handling
.
Subtie
irregularities
in
wheel
alignment

angles
also
affect
stabílity
.
Mixing
different
types
or
sizes
of

tires,
particularly
on
the
same
axle,
can
affect
alignment
and

may
unbalancea
car's
handling
.

Table
b
lists
the
symptoms
of
common
suspension
and

steering
problems
and
their
probable
causes,
and
suggests

corrective
actions
.
Bold
type
indicates
the
repair
groups

where
applicable
test
and
repair
procedures
can
befound
.

SUSPENSION
AND
STEERING
TROUBLESHOOTING

300-8



SUSPENSION,
STEERING
AND
BRAKES-GENERAL

Tableb
.
Suspension
and
Steering
Troubleshooting

Symptom



1



Probable
cause
Repairs
(Repair
Groups
shown
in
bold)

Car
pulís
to
one
side,
wanders



a
.
Incorrect
tire
pressure



a
.
Check
and
correct
tire
pressures
.
020
b
.
Incorrect
wheel
alignment



b
.
Check
and
adjust
wheel
alignment
.
320
c
.
Faulty
brakes
(pulls
only
when
braking)



I
c
.
Check
for
sticking/damaged
front
caliper
.
340

Steering
heavy,
poor
return-



a
.
Worn
upper
strut
bearing(s)



a
.
Replace
strut
bearings
.
310
to-center



b
.
Incorrect
tire
pressure



b
.
Check
and
correct
tire
pressures
.
020
c
.
Power
steering
system
faulty



c
.
Check
power
steering
fluid
level
.
Test
system
pressure
.
320

Front-end
or
rear-end
vibra-



a
.
Worn
strut
cartridgesor
shock
absorbers



a
.
Replace
strut
cartridges
.
310,
330
tion
or
shimmy



b
.
Worn
suspension
bushings
(control
arm
or
trail-



b
.
Replace
worn
bushings
.
310,
330
ing
arm)
c
.
Worn
front
suspension
ball
joints
(control
arm,



c
.
Replace
worn
ball
joints
.
310
steering
arm
orsteering
tie-rod
end)d
.
Unbalanced
or
bent
wheels/tires



d
.
Balance
tires
.
Check
tiresfor
uneven
wear
pat-
terns
.
Check
wheels
for
damage
.
e
.
Loose
wheel
lug
boits



e
.
Tighten
lug
boits
to
proper
torque
.

Poor
stability,
repeated
bounc-
I
a
.
Worn
strut
cartridgesor
shock
absorbers



I
a
.
Replace
strut
cartridges
.
310,
330
ing
after
bumps,
suspension
bottoms
outeasily

Suspension
noise
(especially



a
.
Worn
front
upper
strut
bearings



a
.
Replaceupper
strut
bearings
.
310
over
bumps)



b
.
Loose
front
strut
cartridge



b
.
Check/tighten
strut
cartridge
collar
nut
.
310
c
.
Worn
suspensionbushings
(control
arm
or
trail-



c
.
Replace
worn
bushings
.
310,
330
ing
arm)d
.
Worn
stabilizer
bar
rubber
mounts



d
.
Replace
stabilizer
bar
rubber
mounts
.
310,
330
e
.
Loose
suspension
crossmember



e
.
Check
crossmember
for
damage
.
Tighten
mounting
boits
.

Uneven
ride
height



a
.
Incorrect
coil
springs



a
.
Measure
ride
height
and
replacesprings
as
re-
quired
.
310,
330
b
.
Bent
or
damaged
suspension
components



b
.
Inspect,
repair/replace
asnecessary
.
310,
330
c
.
Sagging
coil
springs



c
.
Measure
ride
height
and
replace
springs
as
re-
quired
.
310,
330

Wheel
noise,
continuous



I
a
.
Worn
wheel
bearing



I
a
.
Replacewheel
bearing
.
310,
330
growling,
may
be
more
notíce-
able
when
turning

Steering
loose,
imprecise



a
.
Incorrect
tire
pressure



a
.
Check
and
correct
tire
pressures
.
020
-



b
.
Loose
steering
gearmounting
bolt(s)



b
.
Inspect
and
tighten
boits
.
320
c
.
Worn
tie
rodend(s)



c
.
Replace
tie
rod(s)
and
align
wheels
.
320
d
.
Faulty
front
wheel
bearing



d
.
Replace
wheel
bearing
.
310
e
.
Worn
or
damaged
steering
gear



e
.
Adjust
or
replace
steering
gear
.
320
f
.
Worn
tires



f
.
Replace
tires
.
010

SUSPENSION
AND
STEERING
TROUBLESHOOTING